This invention relates to liquid crystal modulators and more particularly to polymer dispersed liquid crystal (PDLC) modulator structures. (PDLC may be a mixture of hydroxyl polyacrylate with the TL-series of liquid crystal, where the hydroxyl group is crosslinked by polyisocyanate).
PDLC modulators are used to test thin film transistors in the liquid crystal display (LCD) industry. Modulator lifetime improvement is one of the major objectives in PDLC modulator research and development. Due to the close proximity of components relative to panels under test, PDLC modulator structures are subject to damage in normal use, which severely curtails useful life.
An existing 131 mm square PDLC modulator build on BK-7 optical glass is known wherein the active surface is protected by a thin film (about 6 μm) of polyester (such as Mylar film from Dupont of Wilmington, Del.). Due to the softness of the polyester film, its surface is prone puncture and scratch damage, so that the modulator lifetime has become an issue. The major modulator damage modes include 1) pellicle peeling, 2) particle penetration, and 3) scratching. These damage modes render the modulators useless after relatively short periods of time. As use of PDLC modulators increases, it has become urgent to develop a more robust modulator structure.
Prior solutions have been developed which have proved inadequate. Two specific modes of interest are:
Mechanical Polishing of Glass. This technique involves deposition of dielectric mirror material onto a glass substrate. The glass was then laminated onto NCAP (nematic curvilinear aligned phase) material with the mirror coating in a sandwich contact with the NCAP material. The glass is then mechanically polished back, leaving a very thin structure. The resulting thin film shows weak mechanical strength (which is thus easy to break) when the finished modulator is used in an applicable system.
Direct Dielectric Mirror Coating. In this technique, dielectric mirror material is deposited by physical vapor deposition directly onto NCAP or PDLC material. While this approach could potentially provide a hard but thin surface on the top of modulator, no data related to modulator durability is available. Moreover, attempts at fabricating such a structure have faced technical challenges, including poor yield.
What is needed is a dielectric-based PDLC modulator that is resistant to damage and a method of manufacture.